Self-adjusting doctor blades

ABSTRACT

The disclosure shows self-adjusting doctor blades pivotally mounted in a blade holder. The blade can adjust itself in position relative to a work surface. The blade can also flex about a pivotal stop thereby minimizing or eliminating edge ripple at the leading edge.

I United States Patent [1 1 [111 3,866,266

Dunlap Feb. 18, 1975 SELF-ADJUSTING DOCTOR BLADES Primar Examiner-Edward L. Roberts 751 t.HldE.Dl,Ab,M. Y 1 i or am un u um ass Attorney, Agent, or Firm-Alfred H. Rosen; Frank A. [73] Assignee: Lodding Engineering Corporation, St i hilper Auburn, Mass. I

[22] Filed: Nov. 9, 1973 21 A l. N 414,196 1 PP 0 [57] ABSTRACT [52] Cl 15/25651 100/174 47 The disclosure shows self-adjusting doctor blades pi v- [51 1 Int Cl D21 3/02 otally mounted in a blade holder. The blade can adjust [58] Fie'ld itself in position relative to a work surface. The blade "100/174: l f can also flex about a pivotal stop thereby minimizing or eliminating edge ripple at the leading edge.

[56] References Cited UNITED STATES PATENTS 10 Claims, 11 Drawing Figures 2,071,035 2/1937 .lenett l5/256.5l

PATENTED FEB 1 8 W5 3; 666.266

SHEET 10F 2 SELF-ADJUSTING DOCTOR BLADES BACKGROUND OF THE INVENTION The art of making bladeholders for doctors and scrapers is old, yet continues to develop. The task of doctoring or scraping a moving work surface, as on a roll or cylinder, for example, presents problems of approach to the load, operational control, and blade wear and replacement, which continue to engage paper makers and others facing the task. In the paper industry, the printing industry, and the textile industry, doctors and scrapers are employed to clean the surfaces of rotating calendar rolls, carding rolls in textile machines, drier cylinders and the like; and scrapers are used to remove a web of paper as in the manufacture of crepe paper (creping doctor). Scrapers (sometimes called knives) are used to remove product from drums in flakers and drum driers used to prepare dried products of various kinds (examples being foodstuffs, pharmaceuticals, chemicals, films solidified from liquids) from 'a starting liquid or paste.

When the surface to be doctored or scraped (working surface) is that of a material soft enough to be damaged by a blade or knife approaching it at an angle that favors digging in, chipping or otherwise injuring the working surface, it is important that the bladeholder control the angle at which the blade engages the work surface during operation, as well as the uniformity of contact between the blade and the work surface during operation. A blade holder which permits the blade in it to dig into the doctored surface at one end, would introduce the danger of injuring the. work surface. I

Blades become heated in use, and tend to develop edge ripple" at the working edge, and many attempts have been made to minimize this effect. Attention has been given to special treatments of the body of blades between the working edge and the back edge, to im prove the thermal qualities. It is important to eliminate the formation of edge ripple during operation, because the occurrence of edge ripple causes non-uniform doctoring and, again, introduces the risk of injuring the doctored work surface.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of bladeholder according to the invention, with a blade in place therein;

FIG. 2 shows a cross sectional view of -FIG.' 1 taken on line 2-2, with the working edge of the blade in contact with a roll surface shown schematically;

FIG. 2A shows an enlarged view of section A of FIG. 2;

FIG. 3 schematically illustrates the basic operation of the invention;

FIG. 4 illustrates how the invention operates to minimize edge ripple;

FIG. 5 further illustrates the correction of edge ripple; 1

FIG. 6 illustrates another embodiment of the invention;

FIG. 7 illustrates a third embodiment of the invention;

FIG. 8 illustrates still another embodiment of the invention;

FIG. 9 is a schematic illustration of an operational effect of the edge ripple correction shown in FIG. 4; and

FIG. 10 illustrates still another embodiment of the invention for controlling blade working pressure during edge ripple correction.

FIGS. 1 and 2 illustrate a practical form of the invention. A doctor back 10 is supportable on pins (not shown) fitting into a pair of holes 11 at each end. The

top surface of the doctor back has three levels 12, 14 and 16, separated respectively at rabbeted surfaces 13 and 15. A blade clamping bar 17 is itself clamped to the second surface 14 by a rigid backing plate 18 which is fastened to the doctor back with screw bolts 19. The clamping bar is flexible and is spaced a small distance from the third surface 16 of the doctor back, and the forward edge 17.] of the clamping bar extends forward of the forward edge 10.1 of the doctor back. A blade 20 having a forward edge 21 and a rear edge 22 fits into the space between the clamping bar 17 and the third surface 16, being loosely slideably fitted in that space. i The portion of the blade which is bounded by the rear edge 22 is held in the blade receiving space by a ball 26 that is seated in a bore 27 opening through the third surface 16 of the doctor back 10. The ball rests on a spring 28 which urges it out of the bore, and protrudes slightly through an aperture 29 in the clamping bar 17.

The blade has a slotted aperture 30 which is in register with the ball 26 when the blade is properly located in the holder. Through this mechanism a blade can be inserted into the holder and will be held in place by the ball 26, but can be withdrawn, if desired. The portion of the blade 20 which is bounded by the forward edge 21 sticks out of the holder 10 and the forward edge 17.1 of the clamping bar 17 can bear on the upper surface (as shown in FIG. 1) of the blade when a force is applied against the lower surface as by a roll 31 in contact with the forward edge 21 when the blade is brought in position for doctoring the roll.

The surface 15 of the rabbet between the second and third surfaces 14 and 16 of the doctor back defines the inner or back wall of the blade receiving space. A stop member 23 is provided in the form of a pin, seated in a bore 23.1 in the doctor back 10, which bore .is generally normal to the second and third surfaces 14 and 16 and opens partly through each, so that the top portion of the pin extends in part forward of the back wall 15 into the blade receiving space. The bore may be relieved around the end portion of the pin in the bladereceiving space, as is shown at 24. The pin 23,thus provides a stop for the rear edge 22 of the blade, holding the rear edge away from the back wall 15 of the blade receiving space. FIGS. 3 and 4 illustrate advantages of this stop.

FIG. 3 is a schematic top view of the device shown in FIGS. 1 and 2. The back edge 22 of the blade 20 is shown in dashed line generally parallel to and spaced from the back wall 15 of the blade receiving space, the dimension of this spacing being established by the distance that the stop member 23 protrudes into the blade receiving space, the pin 23 in this illustration being in a bore which is partly in the region of the third surface 16 and partly in the region of the second surface 14. It will be understood that the pin 23 may be entirely or partly in the region of the third surface 16, and indeed its position may be made adjustable. If the blade-holder 10 is aligned with the axis of the roll 31, then the forward or working edge 21 of the blade should also be in the desired alignment with the surface of the roll that is being doctored. However, misalignment between the bladeholder and the roll is frequently experienced, and in that event the blade 20 is free to align itself with the roll, within a misaligned holder. The back edge 22 of the blade can assume a position which is not parallel to the back wall of the blade receiving space, within limits which are determined by the distance between them.

Doctor blades work essentially by scraping or sliding on a moving surface and this action generates heat or friction along the line of contact, namely the forward edge 21 of the blade 20. Thus, as is well known, during use of doctor mechanisms a temperature gradient AT is established from the forward edge 21 to the back edge 22 of the blade. In consequence, the portion of the blade bounded by the forward edge 21 expands relative to the portion of the blade bounded by the back edge 22. In the art of bladeholders as known up to now, the back edge 22 of the blade is restrained along its entire length. Consequently, thermal expansion of the forward portion gives rise to an annoying result known as edge ripple in which the forward edge 21 of the blade assumes a rippled or a wavy configuration relative to the plane of the blade. The result of the edge ripple is that the blade does not contact uniformly the surface being doctored. There have, of course, been attempts made to minimize edge ripple, one such attempt involving cutting slots in the blade extending from the region of front edge 21 to the region of the back edge 22. In the present invention a far simpler and more effective solution is made available, as is illustrated in FIG. 4. Expansion of the portion of the blade bounded by the leading edge 21 due to the heat of friction simply makes the blade longer at the forward edge.'Since the back edge 22 is free to pivot around the stop 23, the back edge assumes a concave configuration. The source of edge ripple at the working edge 21, namely inability of the back edge 22 to become concave, is removed and edge ripple is very much minimized, if not totally eliminated.

The curved distortion of a blade which is illustrated in FIG. 4 may also be brought about by the forces of friction existing between the blade and the surface 31 during a roll-doctoring operation, separately from the distortion due to AT. Thus, as is shown in FIG. 5, thesurface of a roll 31 (rotating in the direction shown in FIG. 2) exerts force into the blade all along the front edge 21 as is represented by arrows 40 disposed along the front edge. At the same time the stop 23 exerts a counter force on the back edge 22,between its ends, as is illustrated by a single arrow 41. It will be immediately apparent that these forces working together produce deflection of the blade within its plane and around the stop 23, as is illustrated in FIG. 5, thus putting the working edge 21 in tension which in turn further reduces any tendency to form edge ripple at the working edge.

The invention can thus be seen to provide not only novel self-alignment features, but also improvements in the reduction or elimination of working-edge ripple. Some variations of the holder structure which provides these advantages are shown in FIGS. 6, 7 and 8. FIG. 6 schematically illustrates that force can be applied to the back edge 22 of a blade at two points 42 and 43 which are relatively close together and about midway between the ends of a blade. Such force can be applied by a pair of stops likethe stop 23 .orby a pivot bar 45 as is shown in FIG. 7. T hat pivot'bar rests pivotally on the stop 23, to which it may be fastened in a pivotal manner, and it has two contact elements 46 and 47 extending forward to meet the rear edge 22 of the blade 20. There is no particular distance between two contact points that is preferred, but obviously they should not be so far apart that the blade can be deflected inward in the portion that is between them.

FIG. 8 illustrates a somewhat more complex arrangement in which the blade-receiving space is fitted at its back wall 15 with a pivot stop 51 from which a series of toggle links 52, 53 extends in both directions. Means (not shown) such as springs or other resilient material will be employed to exert force represented by arrows 54, 55 for adjusting the limits through which the blade 20 can pivot or bow.

When the blade 20assumes a bowed configuration the ends may tend to recede from the surface being doctored. This is illustrated in FIG. 9 where the central portion of the leading edge 21 is shown in contact with the roll 31 but an end 21.1 is shown out of contact with the surface being doctored. In that figure reference character 22 is reserved for the central portion of the back edge 22 of the blade while reference character 22.1 indicates an end of the back edge. If the clamping bar 17 is sufficiently flexible and has a sufficiently low spring rate,'and if the backing plate is designed to press downward on the clamping bar toward the blade 20, then the clamping bar can urge the blade toward the roll 31 so that the leading edge 21 remains in contact with the surface of the roll throughout its length, including the ends 21.1. Another way to assure complete contact between the leading edge 21 of the blade and the surface of the roll 31 is illustrated in FIG. 10.

FIG. 10 makes use of a mechanism for holding a doctor blade in contact with a roll surface, against forces which tend to create flexure in the blade along the working edge 21. Several possible solutions can be employed involving resilient profiling members which to varying degrees will urge the working edge 21 into contact with a doctored surface under uniform pressure throughout its length. A preferred solution is one like that which is described in US. Pat. No. 3,529,315 of the present inventor and another, which is assigned to the predecessor of the assignee of this application.

FIG. 10 illustrates schematicallya bladeholder 59 having a resilient profiling member 61 essentially according to that patent located in a blade receiving compartment 62 for bearing against a surface 63 of a blade 20 near the back edge 22. The bladeholder has a jaw 66 which bears on the opposite surface of the blade 20, in-

termediate its edges 21 and 22. As is explained in the referenced patent, the profiling member 61 will cause the working edge 21 of the blade to bear against the surface of the roll 31 with substantial uniform pressure along its entire length. One may make use also of pressure control arrangements as described and shown in US. Pat. Nos. 2,914,788 and 3,163,878, both assigned to D.S.T. Pattern and Engineering Company Limited.

I claim:

1. In combination, a generally planar elongated doctor blade having extending in the direction of elongation a forward edge for doctoring a surface in motion transverse to said direction relative to the blade and a back edge spaced from the forward edge by the width of the blade, and a holder for the blade comprising first and second spaced-apart members bounding an elongated blade-receiving space having a length substantially the same as the length of said blade, and a depth less than the width of the blade for receiving a first portion of the blade bounded by the back edge while a secnd portion of the blade bounded by the forward edge sticks out of the holder, throughout the length of both the holder and the blade, and means fixed in the bladereceiving space for stopping said back edge in a limited region intermediate the ends of the blade, said blade being free within prescribed limits to pivot in said holder around said stopping means.

2. A combination according to claim 1 in which said holder includes yieldable displacement means for applying force to urge the second portion of the blade toward said surface with a pressure that is substantially uniform along the forward edge of the blade.

3. A combination according to claim 1 in which said blade is made of a material which expands when heated, such that the first portion elongates relative to the second portion when the blade is heated due to friction between the forward edge and said surface, whereby the back edge of the blade is urged into an increasingly concave configuration, said blade being free within prescribed limits to flex in said holder around said stopping means.

4. A combination according to claim 3 in which said holder includes yieldable displacement-means for applying force to urge the second portion of the blade toward said surface with a pressure that is substantially uniform along the forward edge of the blade.

5. A combination according to claim 1 in which said stopping means includes at least one elongated stop member in the blade-receiving space oriented in a direction transverse to the plane of a blade therein.

6. A combination according to claim 5 including a pivot bar between said back edge and the stop member,

said pivot bar being in pivotal contact at one side with the stop member and having at least two contact elements extending from an opposite side into contact with said back edge.

7. A combination according to claim 1 including resilient restraining means for controlling pivotal motion of said blade.

8. A doctor blade holder having a blade receiving space bounded by top and bottom wall members and a back wall member, and having a blade-receiving opening opposite the back wall, said holder being elongated in the dimension of said back wall, and in said space stop means located forward of the back wall member for contacting the rear edge of a blade when present in said holder and locating said rear edge out of contact with the back wall member, said stop means being re stricted to a minor portion of the length of said space intermediate theends thereof and having bearing means for allowing a blade when present within and extending substantially the full length of said space to pivot around said stop means within said space.

9. A holder according to claim 8 in which said stop means includes a pin oriented from one of the top and bottom walls toward the other.

10. A holder according to claim 8 in which said stop means includes a bar in said space extending part way along the back wall and pivotally contacting the stop means, said bar having contact members extending forward to meet the back edge of a blade when present in said space, the length of said bar being a minor fraction of the length of said holder. 

1. In combination, a generally planar elongated doctor blade having extending in the direction of elongation a forward edge for doctoring a surface in motion transverse to said direction relative to the blade and a back edge spaced from the forward edge by the width of the blade, and a holder for the blade comprising first and second spaced-apart members bounding an elongated blade-receiving space having a length substantially the same as the length of said blade, and a depth less than the width of the blade for receiving a first portion of the blade bounded by the back edge while a second portion of the blade bounded by the forward edge sticks out of the holder, throughout the length of both the holder and the blade, and means fixed in the bladereceiving space for stopping said back edge in a limited region intermediate the ends of the blade, said blade being free within prescribed limits to pivot in said holder around said stopping means.
 2. A combination according to claim 1 in which said holder includes yieldable displacement means for applying force to urge the second portion of the blade toward said surface with a pressure that is substantially uniform along the forward edge of the blade.
 3. A combination according to claim 1 in which said blade is made of a material which expands when heated, such that the first portion elongates relative to the second portion when the blade is heated due to friction between the forward edge and said surface, whereby the back edge of the blade is urged into an increasingly concave configuration, said blade being free within prescribed limits to flex in said holder around said stopping means.
 4. A combination according to claim 3 in which said holder includes yieldable displacement means for applying force to urge the second portion of the blade toward said surface with a pressure that is substantially uniform along the forward edge of the blade.
 5. A combination according to claim 1 in which said stopping means includes at least one elongated stop meMber in the blade-receiving space oriented in a direction transverse to the plane of a blade therein.
 6. A combination according to claim 5 including a pivot bar between said back edge and the stop member, said pivot bar being in pivotal contact at one side with the stop member and having at least two contact elements extending from an opposite side into contact with said back edge.
 7. A combination according to claim 1 including resilient restraining means for controlling pivotal motion of said blade.
 8. A doctor blade holder having a blade receiving space bounded by top and bottom wall members and a back wall member, and having a blade-receiving opening opposite the back wall, said holder being elongated in the dimension of said back wall, and in said space stop means located forward of the back wall member for contacting the rear edge of a blade when present in said holder and locating said rear edge out of contact with the back wall member, said stop means being restricted to a minor portion of the length of said space intermediate the ends thereof and having bearing means for allowing a blade when present within and extending substantially the full length of said space to pivot around said stop means within said space.
 9. A holder according to claim 8 in which said stop means includes a pin oriented from one of the top and bottom walls toward the other.
 10. A holder according to claim 8 in which said stop means includes a bar in said space extending part way along the back wall and pivotally contacting the stop means, said bar having contact members extending forward to meet the back edge of a blade when present in said space, the length of said bar being a minor fraction of the length of said holder. 